The present invention relates to projection display systems and particularly to controlling the lamp focus and brightness in such systems.
The lamp used in projection display systems requires periodic adjustment for optimum light distribution on the display screen and for maximum overall brightness of the projected image. This adjustment is normally carried out by skilled technicians, and as a result has often been neglected resulting in projectors being operated with less than optimal performance. This is particularly true in the case of modern spatial light modulator projection systems, where the lower f/# of the optics makes the sensitivity to lamp focus even greater.
Some spatial light modulator projection systems have addressed the lamp focus issue by placing a detector near the stop of the optical system""s relay lens to measure the overall system brightness and then adjusting the brightness based on this data. However, this approach completely ignores the brightness distribution issues that are so critical in such systems.
What is needed is a method that collects data for both the light distribution and brightness level in a projection system and uses this data to automatically adjust the lamp brightness and position for optimal projection performance.
This present invention discloses methods and structures for providing automated lamp focus and brightness control in spatial light modulator (SLM) based projection display systems.
One embodiment discloses a method of sampling the light output and distribution of the projector without having to measure the screen surface. These systems typically use relay optics to focus light from an integrator on to the focal plane of spatial light modulators. The relay optical system is folded using mirrors to maintain co-linearity between the light input and output. In the present invention, one of these folding mirrors is used as a sampling filter, where a small fraction of the light that strikes the surface of the partial mirror passes through it. A separate lens is then used to focus this faint image, which is identical to the primary projection image except for brightness, on to a detector. The brightness level of this sampled image is then correlated with the overall system brightness. The output of the detector is connected to a micro-controller, which is used to determine the light distribution at selected points in the image and the brightness of the image. The output of the micro-controller then drives control hardware for positioning (focusing) the lamp and adjusting the brightness of the image.
Another embodiment discloses a method by which an array of light sensors are embedded in perforations in the surface of a display screen to provide input data to a micro-controller, which is used to determine the light distribution and brightness of the system and to drive lamp position (focus) and brightness control hardware. In this case the sensors are spatially located at selected points on the surface of the screen to directly detect the light hitting the display screen.